Method and apparatus for sizing of discrete particles in a fluid medium



July 15, 1969 R. 1'. HUKKI 3,455,450

METHOD AND APPARATUS FOR SIZING 0F DISCRETE PARTICLES IN A FLUID MEDIUM Filgd Feb. 15, 1967 4 Sheets-Sheet 1 INVENTORI RISTO TAPANI HUKKI.

ATTORNEYS INVENTORZ AT TORNE YC 4 Sheets-Sheet 2 I 5 2 A A,

g s 1 v g v w I 0 B W M 4 5 0/0 2,. L 5 m. x x w y .43 V N 1r l I l July 15, 1969 R. T. HUKKI METHOD AND APPARATUS FOR SIZING OF DISCRETE PARTICLES IN A FLUID MEDIUM Filed Feb. 15. 1967 RISTO TAPANI HUKKI.

BY. MALL/NCKROD 8 MAL/.INC/(RODT July 15, 1969 R. T. HUKKI 3,455,450

METHOD AND APPARATUS FOR SIZING OF DISCRETE PARTICLES IN A FLUID MEDIUM Filed Feb. 15, 1967 4 Sheets-Sheet 5 INVENTORI RISTO I TAPANI HUKKI.

ATTORNEYS July 15, 1969 T. HUKKl 3,455,450

7 METHOD AND APPARATUS FOR SIZING OF DISCRETE PARTICLES IN A FLUID MEDIUM Filed Feb. 15, 1967 4 Sheets-Sheet 4 W nunnununnnnut INVENTORI RISTO TAPANI HUKKI BY: MALL/NC/(RODT 8 MALL/NCKRODT AT TORNE YS United States Patent Ohio . Filed Feb. 15, 1967, Ser. No. 616,264

Int. Cl. B04c 7/00; B0311 3/00 US. Cl. 209-444 16 Claims ABSTRACT OF THE DISCLOSURE A method of efiectively separating the sands fraction, i.e. larger particles of a material, from the fines fraction, i.e. smaller particles, in a wet or dry sizing process, and apparatus therefor.

In a quality control section at least a portion of the material being sized is spread into at least one annular layer and a wash medium is forced over each such layer to pick up a fines-bearing portion of the material. The material so picked up is carried upwardly along an upright axis and the fines and sands which are not picked up by the wash medium are separately discharged downwardly.

When the quality control section is used with a sizing unit, such as a classifier or hydrocyclone, fines will be removed as the material being sized passes through the sizing unit, and the fines-containing material subsequently removed by the quality control section of the invention, together with the Washing medium used, will be directed into the sizing unit for further separation of the fines fraction contained therein from the sands fraction. By repeatedly removing fines-bearing portion of the material and recirculating it as many times as is desired, the desired amount of separation can be obtained.

Brief summary of the invention This invention relates to wet and dry sizing of discrete particles using a fluid medium. More particularly it is directed to an improved method and apparatus for quality control of the sands fraction produced in a continuous wet or dry sizing process.

In conventional industrial sizing processes, two products are separated, i.e. the fine product or fines and the coarse products or sands. It is well known that all industrial sizing processes, both wet and dry, still remain unsatisfactory, especially with regard to the sharpness of separation obtained.

Attempts to remove the retained fines from the sands have already been made. These have included, for example, processes involving the spraying of wash water on the sand bed in an open mechanical classifier, or through the bed spread over the wide bottom surface of such an apparatus; the use of multiple stage hydrocyclones; the introduction of wash water into the sand cone of a hydrocyclone via one or several tangentially placed tubes; and the circulation of gas mediums, in various ways, across the sand beds of dry separation units. However, in spite of these and other processes no satisfactory method and apparatus have heretofore been developed to produce sands of high quality, i.e. not containing undesired amounts of fines.

The present invention describes an improved method and a corresponding apparatus capable of controlling the quality of the sands fraction in a simple way, to any desired extent. That is, it provides a method and apparatus for removing virtually any desired percentage of the fines fraction from the sands fraction.

3,455,450 Patented July 15, 1969 "Ice Principal features of the method of the present invention are found in the steps of forcing at least part of the material to be separated into an annular layer or layers rotated in a helical manner about a non-rotating core placed on the axis of apparatus in which separation is to take place;

directing a wash medium from an outside source across the said annular layer or layers, with the flow rate of the wash medium supplied to each layer being regulated, as desired;

diverting a portion of the fiow of the Wash medium, with removed solids, from the top part of each layer into a common upwardly directed stream while passing the non-removed solids with the helical main stream downwardly;

passing the upwardly directed stream to an upper level in such a way that the said stream is maintained separated from the stream of uncleaned sands, i.e. material being separated, surrounding it;

returning the solids carried by the common, upwardly directed stream to the original stream of material being fed into a sizing unit for further separation;

discharging the separated fines fraction of the returned material with the final fines product;

returning the separated coarse or sands fraction of the said returned material for further cleaning with the uncleaned sands fraction; and

collecting and discharging the separated coarse fraction,

i.e., cleaned sands, below the level of separation.

As a further step in the process, cleaning of the uncleaned sands can be repeated any desired number of times within a single apparatus constructed for the purpose.

To greatly minimize the possibility that fines will escape downwardly with the sands, the downward flow of the Wash medium must be reduced to a practical minimum. To accomplish this the cleaned sands are collected below the lowermost level of separation into a non-rotating sand bed such that sands are discharged from the bottom of the bed at the same rate as new sands are accumulating on the top of the bed. Downward flow within the said bed from its top section to its bottom section is prevented but peripheral flow is maintained. Provision is made for centrally withdrawing wash medium, with retained fines bearing material, from the top of the cleaned sand bed.

The rate of discharge of final cleaned sands is regulated in accordance with the characteristics of the sand bed, which is located below the lowermost level of separation.

The apparatus for quality control of the sands fraction according to the method described above consists essentially of two sections; an upper quality control section and a lower sands collecting compartment. The two sections, together, preferably form the bottom part of a continuously operating hydraulic or pneumatic sizing unit to which they are attached. The sizing unit itself provides conventional means for feed introduction, for initial separation of fine and coarse fractions, and for discharge of the fines and sands products. The portion of the sizing unit through which the clean sands product is discharged is attached to the uppermost part of the quality control section.

Principal features of the quality control apparatus of the invention include: I

a shell consisting of a substantially cylindrical tube, prefearbly made up of a pack of coaxial, superimposed rings jointly forming the said tube;

a core fixed within the shell and preferably consisting of a pack of coaxial, superimposed, conical, core pieces held separated by spacers;

an annular space between the shell and the core;

means to admit a wash medium, which may be a liquid or a gas, into the said annular space; inwardly and upwardly directed channels formed by the core pieces and the spacers;

central openings in the core pieces, jointly forming a passageway about the vertical axis of the vessel;

a top piece having a bore that extends the passage-Way upwardly to a desired elevation, and

means to assemble the parts together and to support the core coaxially within the shell.

Principal features of the lower sands collecting compartments include a cylindrical collecting vessel; a disc within the said vessel preventing central discharge of material thereabove; and a plurality of, e.g. radial, vanes supporting the said disc.

Objects of this invention are to provide a new and useful method and an apparatus for continuous quality control of the sands fraction in connection with any suitable size separation process. With minor changes the apparatus can be applied equally well for wet and dry sizing. Furthermore, the apparatus is compact in size and rugged and simple in construction. Because the washing of the sands fraction can be repeated any desired number of times, the finals sands of extremely high quality can be obtained.

There is shown in the accompanying drawings specific embodiments of the invention representing what are presently regarded as the best modes of carrying out the generic concepts in actual practice. From the detailed description of these presently preferred forms of the invention, other more specific objects and features will become apparent.

The drawings FIG. 1 is an isometric view partly in vertical section of the top piece included in the apparatus of this invention;

FIG. 2, a similar view of a typical spacer;

FIG. 3, a similar view of the corresponding core piece;

FIG. 4, a similar view of the corresponding outer ring;

FIG. 4a, a view corresponding to that of FIG. 4, but showing another embodiment of outer ring;

FIG. 5, a vertical axial section showing the details of a multiple step, quality control section constructed from the basic elements shown in FIGS. 1, 2, 3 and 4, together with a sands collection compartment;

FIG. 6, a similar view showing the sands quality control section and the sands collecting compartment attached to a hydraulic sizing apparatus; and

FIG. 7, a similar view showing the sands quality control section and the sands collecting compartment attached to a hydrocyclone.

Detailed description As is best seen in FIG. 1, top piece 1 consists essentially of a conical base 2 attached to open cylindrical tube 3. For convenience of assembly top piece 1 is provided with, e.g. two or more, conveniently shaped openings 4 through which connecting bolts can be inserted.

Core piece 5, shown in FIG. 3, includes a conical shell 6, a central opening 7 of substantially the same diameter as tube 3, and openings 8 for connecting bolts. When a number of these core pieces are grouped together, pairs of spacers 9, FIG. 2, are placed between adjoining core pieces and around the bolts that hold the assemblage together.

As is illustrated in FIG. 4, each outer ring 10 consists of a cylindrical wall 10a provided with one or more, preferably tangential, medium-inlet means 11 that may include nozzles, not shown, of any desired type. If desired, rings 10 may also be provided with inner skirtlike extensions 12, FIG. 4a, that slope inwardly. In such case, the inlet means 11 are preferably arranged to open into the inverse, ring-shaped slot 12a defined by the inner cylindrical wall of ring 10 and the bottom surface of extension 12. To enable rings 10- to be conveniently assembled in a pack, the top and bottom surfaces of each are provided with mating grooves 101) and ridges 100, respectively.

In FIG. 5, there is shown the detailed construction of a multiple step, quality control section 13 and a joining sands collecting compartment 14. Essentially, the quality control section consists of a pack of coaxial, superimposed rings 10 jointly forming a cylindrical shell of the section, and of another pack of coaxial, superimposed, conical, core pieces 5 that jointly form the core of the section. Top piece 1 is placed over the uppermost core piece and between the outer shell and the inner core, an annular space 15 is formed. The pack of rings 10 is held tightly together between the bottom flange 16 of a sizing unit and the top flange 17 of the sands collecting compartment 14, by bolts 18.

The core is supported on a base plate 19 that is provided with a number of peripheral openings 20 and central opening 21. A conical member 22 on the base plate extends into the lowermost core piece 5 to hold the core centered and the core is held together by bolts 23, that extend through holes 4 and 8 in the top piece 1 and core pieces 5, respectively. Spacers 9 define conical flow channels 24. Openings 7 in core pieces 5 jointly form a passage-way 25 about a vertical axis of the apparatus, and tube 3 extends the passage-Way upwardly to a desired elevation.

The sands collecting compartment 14 shown in FIG. 5 includes a preferably cylindrical vessel 26, having therein a horizontally placed circular plate 27 of smaller diameter than the inside diameter of vessel 26. An annular flow channel 28 is formed between the interior wall of vessel 26 and the periphery of plate 27 and a desired number of radially placed vanes 29 support the plate. A discharge valve 30 controls flow from a bottom port of the vessel 26.

A separate system is used to introduce additional Wash medium beneath plate 27. This system includes an inlet pipe 31 and a downwardly pointing nozzle 32.

Vibrator 33 of any well known type can be attached to any selected place on the outside of the sand cleaning apparatus. When so equipped, the sand cleaning apparatus is preferably separated from the main body of the sizing vessel by a flexible joint (not shown).

It should be clear that the basic parts shown in FIGS. 1, 2, 3, and 4 can be assembled for any desired multiplestep cleaning system. The said parts are preferably made of rubber, but other wear resisting materials may also be used. Vessel 26 may be made of transparent material, or can be provided with a window to allow visual observation of the process carried out therein.

In FIG. 6 there is shown a hydraulic classifier 34 provided with the sands quality control apparatus of the type heretofore described. The upper structure, as such, represents the essential features of a classifier of known type. The classifier includes a feed pipe 35, a feed inlet tube 36, a rotating shaft 37 that carries a distribution plate 38, a hollow extension 39, an impeller 40, an ejector 41, a laminar flow vane zone 42, an overflow weir 43, and a collecting launder 44 for receiving the fines fraction. A drainage pipe 45, having a valve 45a therein, is an addition at the lower end of the classifier. Cleaning section 13 and the sand collector compartment '14 attached to the bottom of the main vessel include the essential features previously described. In the hydraulic apparatus shown, a wash medium such as water is supplied through pipe 46 under constant pressure. Flow to individual rings 10 is through lines 11 and is controlled by valves 47.

FIG. 7 shows the construction of a hydrocyclone equipped with a sands quality control apparatus of the type heretofore described. Essentially, the hydrocyclone consists of a cylindrical housing 48, substantially conventional feed and overflow pipes, 49 and 50, respectively, and the quality control section 13 and sands collecting compartment 14. The housing of the hydrocyclone is constructed of a number of similar, cylindrical, rubber-lined elements 51, a feature that simplifies the manufacturing of the unit and makes rapid changing and reassembling of parts possible. The hydrocyclone is also provided with a conical control member 52 situated below the overflow entrance opening and means 53 to adjust the vertical position of member 52 from the outside of housing 48. Means for wash water distribution can be arranged substantially as shown in FIG. 5.

The present invention is directed to an improved method and apparatus for quality control of the sands fraction produced in a continuous wet or dry sizing process. Accordingly, it is understood that suitable method and means already exist for the primary separation producing such sands fraction, which is then processed according to the principles of this invention. The operation of the quality control apparatus will be hereinafter illustrated with reference to the hydraulic units shown in FIGS. 5, 6, and 7. In pneumatic units, cleaning of the dry sands fraction follows the same essential steps, but a gaseous Wash medium is used.

In the apparatus of FIG. 6', the original feed material to be classified is introduced via pipe 35 and tube 36 into the middle section of classifier 34. In the conical part of the classifier housing the pulp is brought into forced rotational motion about the vertical centerline of the vessel, primarily by the rotating impeller 40. The fines fraction flows upwardly via zone 42, is reclassified under laminar flow conditions within the said zone, and is discharged over weir 43 into launder 44. The coarse, impure sand fraction is continuously introduced in a helical manner into the downwardly leading, annular space 15 defined by the interior of the pack of shell rings 10 and the pack of core pieces 5.

Within cleaner section 13, the sands are now roughly classified in such a :way that the coarsest and heaviest grains accumulate towards the inner wall of the shell, while the fines and/or lighter grains with the bulk of available wash medium accumulate toward the center portion of the rotating materials and move in layers into the spaces between the stacked core pieces 5. Wash medium admitted via inlet means 11 situated on the various superimposed levels is forced to flow across the said layer or layers from outside inwardly toward the region of minimum pressure. The flow rate or rates of wash medium from outside pipe 46 are controlled, e.g. by valves 47 or by any other manually or automatically adjusted means known to a person skilled in the art. The inward and upward flows of wash medium with suspended solids therein are directed through channels 24 into one common, upwardly-directed stream in passage-way 25, while the non-suspended particles are passed downwardly in annular passage 15 as a helical, main stream of sands. The upward stream is directed, within passageway 25 and its extension 3, to a desired elevation within the classifier housing. The core assemblage separates the upwardly flowing stream from the layers of downwardly flowing uncleaned sands surrounding them. The further flow of the suspension via extension 39 is assisted by ejector 41, which acts as a pump and which also sprays the suspension over a 360 area below a curtain inflowingfeed pulp ejected similarly over a 360 area by distribution plate 38.

Wash medium admitted via inlets 11 and the removed fines are not only moved through the uncleaned sand bed existing in the conical part of the housing of the classifier in a natural way, but are also brought up to a level where they reach the primary separation zone and where the said primary separation is greatly assisted by the added available wash medium. The returned material is thus further subjected to separation along with the original material being fed into the classifier. The fines fraction of the returned solids is discharged with the final fines product as already explained, while the separated coarse fraction is recirculated for further cleaning along with the newly added uncleaned sands fraction. From the lowermost cleaning step, cleaned sands pass via annular openings 20 into the sands collector compartment 14.

For eflicient removal of the fines from the uncleaned sands, the upwardly returned, suspended fraction must carry a substantial portion of oversize particles as well. In other words, a substantial circulating load must result. Hence, the returning fraction is preferably submitted for renewed sizing operation and is not withdrawn as a separate fines product. As a result, one final fine product and one final coarse product only are ultimately produced.

If a maximum amount of fines are to be removed, the possibilities of the wash medium and fines carried thereby escaping with the cleaned sands must be reduced to a practical minimum. Thus, in FIG. 6, the cleaned sands are collected in vessel 26 such that a distinct, non-rotating, sand bed of substantial volume is formed. From the bottom of the bed the sands are discharged via valve 30 at the same rate as new sands are accumulating on the top of the bed. For eflicient control of the flow conditions within the sand bed it has been observed that a centrally forming conical flow channel within the core of the bed must be prevented. Instead, internal flow from the top part of the sand bed to the bottom part is maintained preferably adjacent to the interior wall of vessel 26. This is accomplished by use of a circular disc 27 which defines an annular flow channel 28 for the settling sands. Radial vanes 29 not only support disc 27, but also help in preventing rotation of the sand bed. Material flow within the cleaning section and within the sands collecting compartment can be assisted, in desired cases, by vibration obtained by means of vibrator 33.

Some wash medium containing a certain amount of suspended material is separated from the top of the nonrotating sand bed. This suspension is withdrawn, as shown, via central opening 21 to join the main upward stream in passage-way 25.

The operation of the hydrocyclone shown in FIG. 7 is essentially that of any conventional hydrocyclone. With the quality control apparatus, however, multiple step cleaning of the impure sand fraction is accomplished and the upward flowing suspension is diverted by conical member 52 into the main pulp layer that is rotating about the centerline of the vessel. This. is essential because the upwardly flowing stream also carries oversize particles that should not be discharged with the overflow product. Member 52 forces the returning material to be reclassified within the primary separation zone of the hydrocyclone and the vertical position of member 52 can be easily adjusted by conventional adjustment means 53.

In FIG. 5, there is shown a preferred automatic sands discharge control system. With this apparatus, a controlling impulse is obtained from within vessel 26. This impulse is generated in response to a detected characteristic of the non-rotating sand bed within the vessel. Although various bed characteristics can be used, the preferred one is the level of the top surface of the sand bed. A change in its position can be detected by apparatus 54, which may be a bubble tube, a vibrator, a nuclear gauge, an ultrasonic detector, or other means well known to a person skilled in the art. The impulse is transformed, as required, to operate a regulating valve 5, or a system of valves (not shown), introducing wash medium at desired rates via inlet pipe 31 and nozzle 32 into the throat of the valve 30, which has a pre-set opening. If the sand level is correct, a balancing amount of wash medium is introduced via nozzle 32. If the sand level is below normal, the flow rate of the wash medium is retarded and if the level is above normal, the flow rate is increased. The essential feature here is that the automatic regulation of the rate of sand discharge is based on a relatively simple regulation of a medium stream rather than on a much more complicated adjustment of the valve opening.

The improved means for quality control of the coarse fraction described in this specification can be applied equally as well for similar purposes in a great variety of sizing and separation apparatus of both wet and dry types. These include a variety of hydraulic and pneumatic cyclones, wet and dry classifiers equipped with mechanical rotating means and having substantially conical or equivalent means for the discharge of the coarse product, and many pneumatic classifiers such as those described by Taggart in Handbook of Mineral Dressing, John Wiley & Sons, New York (1945), pages 9-20 to 9-37, where the apparatus includes a conical lower part for the collection of the sand product. Heavy liquids and heavy suspensions may also be used as a wash medium in wet separators.

The present invention is not limited to use in any particular field of the industry. The method and apparatus described in this specification can be used in wet and dry sizing and separation of ores and minerals, in dry sizing of ground cement, and in dry and wet sizing of many other natural or artificial inorganic, organic, or metallic discrete solids. It should also be understood that in all cases where the sands consist of grains of low and high specific gravity, the high specific gravity grains will concentrate into the washed sands fraction, as is well known to the person skilled in the art.

The utility of this invention can be seen from the following experimental data:

In wet sizing, on pilot plant scale, in an apparatus constructed essentially as shown in FIG. 6 and operated at a feed rate of about 5 tons per hour of ground mineral pulp containing 3035% solids by weight, the size distribution of the sands fraction in four parallel Tests 1-4 is as indicated below. Tests 1 and 2 were carried out without the sands quality control section, using a classifier having a sand cone equipped with conventional conical sand discharge means and including means for tangentially adding wash water into the sand oone. In Tests 3 and 4 the same apparatus was used, but it was equipped with a 5-ring sands quality-control section of the type described herein. In Test 5 the same apparatus was used, but with the specific objective of obtaining sands of extremely high quality. The results were:

When plotted on a logarithmic paper showing the percent passing on the ordinate and the size on the abscissa, each sands product is represented by .a curve having a substantially straight-line section for the range of finer size classes. The slopes of the said straight-line sections of sands products obtained, e.g. with industrial hydrocyclones, seem to vary from values as low as 0.6 up to about 1.6. In tests performed with the apparatus including the sands quality-control means described in this invention cleaned sands characterized by slopes from 2.5 up to 6 are obtained. It is seen that while the sands reported for Tests 1 and 2 are quite conventional, the sands reported in Tests 3, 4 and 5 have characteristics not previously obtained.

Whereas this invention is here described and illustrated with respect to certain forms thereof, it is to be understood that many variations are possible.

I claim:

1. A method of controlling quality of the sands fraction produced in a continuous wet or dry separation process operating on a material made up of both fine and coarse discrete particles, comprising the steps of flowing at least a portion of said sands fraction from such a process downwardly into a vertically-stacked plurality of annular streams of wash fluid to produce a helical downward flow that tends to carry a sands component of said sands fraction along its outer periphery and a fines component thereof along a plurality of inner peripheral flows corresponding to said annular streams, respectively; flowing the said fines component from said inner peripheral flows upwardly along mutually independent and segregated paths that converge toward the vertical axis of said annular streams and of said downward flow of said sands fraction; merging along said axis the said inner peripheral flows of said fines component to form a single upwardly flowing stream of said fines component wholly segregated from the downflowing sands component; recirculating to said separation process the merged inner peripheral flows of the said fines component; and separately discharging the said sands component downwardly from the said flows of the fines component.

2. A method according to claim 1, further comprising collecting the cleaned sands component into a non-rotating sand bed; discharging the sands from the bottom of the bed at the same rate as additional sands are accumulating on the top of the bed; preventing central flow of said sand bed while maintaining downward flow at the periphery of the sand bed.

3. A method according to claim 2, further withdrawing separated surplus wash fluid and any fines therein from the top of the sand bed and directing them into the single upwardly flowing stream of fines component.

4. A method of separating fines from sands in a material made up of both fine and coarse discrete particles, comprising the steps of flowing such a material down- *wardly into a verticallystacked plurality of annular streams of wash fluid to produce a helical downward flow that tends to carry a sands component of said material along its outer periphery and a fines component thereof along a plurality of inner peripheral flows corresponding to said annular streams, respectively; flowing the said fines component from said inner peripheral flows upwardly along mutually independent .and segregated paths that converge toward the vertical axis of said annular streams and of said downward flow of said material; merging along said axis the said inner peripheral flows of said fines component to form a single upwardly flowing stream of said fines component wholly segregated from the downflowing sands component; and separately discharging the said sands component and said upwardly flowing stream of the fines component.

5. A method according to claim 4, further comprising collecting the cleaned sands component into a non-rotating sand bed; discharging the sands from the bottom of the bed at the same rate as additional sands are accumulating on the top of the bed; preventing central flow of said sand bed while maintaining downward flow at the periphery of the sand bed.

6. A method according to claim 5, further comprising withdrawing separated surplus wash fluid and any fines therein from the top of the sand bed and directing them into the single upwardly flowing stream of fines component.

7. Apparatus for separating fines from sands in a material made up of both fine and coarse discrete particles, comprising a shell in the form of a substantially cylindrical tube; a core in the form of a pack of coaxial, superimposed, conical core pieces spaced to provide inwardly and upwardly directed conical channels between the core pieces, there being an annular space between the shell and the core; means for directing streams of Wash fluid tangentially into said annular space at the respective channels; central openings in the core pieces jointly forming a passageway along the vertical axis of said shell; means supporting the core within the shell; means for the discharge of fines at the top of said shell; and means for discharging sands at the bottom of said shell.

8. Apparatus according to claim 7, in the form of a quality control section for attachment to the sands fraction discharge of hydraulic or pneumatic sizing equipment adapted for continuous operation.

9. Apparatus according to claim 7, wherein the shell is formed by a pack of superimposed, coaxial rings.

10. Apparatus according to claim 7, additionally including a sands collecting compartment.

11. Apparatus according to claim 10, wherein the sands collecting compartment comprises .a cylindrical vessel; a disc within the vessel and defining, with the interior wall of the vessel, a peripheral flow channel; a discharge port leading from the bottom of the vessel; and a plurality of upstanding radial vanes supporting the disc Within the vessel.

12. Apparatus according to claim 10, further including a central flow channel interconnecting the passageway and the interior of the sands collecting compartment.

13. Apparatus according to claim 10, further including means to vibrate the collecting compartment.

14. Apparatus according to claim 10, further including means to regulate the sands discharge means automatically; and control means operated by a signal responsive to .a characteristic of the material within the sands collecting compartment to regulate said sand dis charge means.

15. Apparatus according to claim 14, further including a valve controlling flow through the sands discharge means; and means to inject a fluid wash medium at an automatically controlled rate into the through passage of said valve.

16. Apparatus according to claim 7, further including means to vibrate the apparatus.

References Cited UNITED STATES PATENTS 1,071,715 9/1913 Deister 209158 2,102,525 12/1937 Freeman 209211 2,252,581 8/ 1941 Saint-Jacques 209144 2,494,465 1/ 1950 Watson 209-144 2,796,947 6/1957 Berg 209139 X 2,829,771 4/1958 Dahlstrom 209211 3,351,195 11/1967 Kukki 209158X FOREIGN PATENTS 518,063 6/ 1928 Germany. 554,038 3/ 1958 Canada.

HARRY B. THORNTON, Primary Examiner ROBERT HALPER, Assistant Examiner US. Cl. X.R. 

